Re: [PATCH] Revert "serial: 8250: Fix reporting real baudrate value in c_ospeed field" - Greg Kroah-Hartman

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Johan Hovold <johan@kernel.org>
Cc: "Jiri Slaby" <jirislaby@kernel.org>,
	linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org,
	"Pali Rohár" <pali@kernel.org>
Subject: Re: [PATCH] Revert "serial: 8250: Fix reporting real baudrate value in c_ospeed field"
Date: Thu, 7 Oct 2021 16:21:30 +0200	[thread overview]
Message-ID: <YV8CavX93a8XCSJP@kroah.com> (raw)
In-Reply-To: <20211007133146.28949-1-johan@kernel.org>

On Thu, Oct 07, 2021 at 03:31:46PM +0200, Johan Hovold wrote:
> This reverts commit 32262e2e429cdb31f9e957e997d53458762931b7.
> 
> The commit in question claims to determine the inverse of
> serial8250_get_divisor() but failed to notice that some drivers override
> the default implementation using a get_divisor() callback.
> 
> This means that the computed line-speed values can be completely wrong
> and results in regular TCSETS requests failing (the incorrect values
> would also be passed to any overridden set_divisor() callback).
> 
> Similarly, it also failed to honour the old (deprecated) ASYNC_SPD_FLAGS
> and would break applications relying on those when re-encoding the
> actual line speed.
> 
> There are also at least two quirks, UART_BUG_QUOT and an OMAP1510
> workaround, which were happily ignored and that are now broken.
> 
> Finally, even if the offending commit were to be implemented correctly,
> this is a new feature and not something which should be backported to
> stable.
> 
> Cc: Pali Rohár <pali@kernel.org>
> Signed-off-by: Johan Hovold <johan@kernel.org>
> ---
>  drivers/tty/serial/8250/8250_port.c | 17 -----------------
>  1 file changed, 17 deletions(-)

Argh, sorry I missed this, good catch.  I'll go queue this up now,
thanks.

greg k-h